Perl learning notes 9 Regular Expression Processing text

1. Replacement

S/pattern/replace/; # returns the Boolean value of whether the replacement is successful.

You can use capture variables, such as S/(\ W)/$1/

If the matching fails, no processing is performed.

2. delimiters

For delimiters without left or right, repeat them three times, for example, S //, s ###

There are two pairs of delimiters with left and right points. One pair of include mode and one pair of replace strings can be different. For example: s {}{}, s [] {}, S <> []

3. Optional Modifier

/G can be replaced globally, replacing all matched strings, such as: S // G

/S: Make. Match All characters

/I: case-insensitive

4. Bind Operators

$ File_name = ~ S # ^. * # s; # Remove all UNIX paths

5. Escape Operators

\ U: Convert all to uppercase, or end with \ e

\ L: Convert all to lowercase, or end with \ e

\ U: The next character is converted to uppercase

\ L: the subsequent qualification characters are converted to lowercase letters

Can be used together, \ U \ L all to lowercase, the first letter is capitalized

The preceding operators can be used in double quotation marks.

6. Split string: Split

@ Fileds = Split/:/, "ABS: SDF: FDD"; # Return result list

When two delimiters are connected together, the fields are split out, and the ending part is omitted.

/\ S +/can be blank, such as: Split/\ s +/, $ some_input; # All blank spaces are treated as a space, omitting the blank fields at the beginning

7. String concatenation: Join

My $ x = join ":",; # The result is $ x = "4: 6: 8: 10 ";

Combined with split, split first and connect with different delimiters.

8. m in the list context //

When M // is used in the context of the list, if the matching succeeds, the list of all captured variables is returned. If the matching fails, an empty list is returned: My ($ first, $ second, $ third) =/(\ s + )/;

The/g modifier can match M // to many places, such:

9. Non-Greedy quantifiers

By default,/Fred. + Barney/matches "Fred" first, and then matches all the remaining strings as ". + ", and then". + "one character is spit out until" Barney "is matched. This is greedy mode.

In + ,*,{},? Add "?", Changes it to a non-Greedy mode, from less to more matching;

/M: Cross-row mode match. After this parameter is added, the line break in the row will be matched;

10. Update multiple files at a time

$ ^ I: indicates the suffix of the backup file. Before the backup is processed, the file is backed up, read from the backup file, and create a file with the same name as the source file to write new information;

11. Online Editing Using command lines

-P: automatically generates a small program, while loop

-I. Bak: Backup File Name

-W: open warning

-E: Tell the program the code behind it.

Fred *. DAT: file to be processed